The Internet is a means for communications that users can utilize extremely easily and at low cost. However, as the Internet has originally been prepared for open communications and has been utilized for this purpose, the Internet is not suitable as information exchanging means in the field of business-to-business transactions (B2B), i.e., transactions between companies, where secrecy protection of information is required like corporate information and medical information. Therefore, in order to secure safety of communications by overcoming drawbacks of the Internet, various security means have been developed so far.
However, the conventional security means in the Internet have had such problems that the cost of introducing these means is high, and that these means are so complex that it is not easy to use them.
Further, in the case of using a simple encryption system like the SSL (Secure Sockets Layer) that has been widely used in the Internet and that can be introduced relatively easily, this system has had a problem that encryption keys can be relatively easily stolen by third parties.
In the information exchanges like the B2B, there are many cases where the XML (Extensible Markup Language) of which standardization has been progressed by the WWW consortium (W3C) is used as a data description language. Information prepared in the XML uses elements as a basic unit. The “element” consists of an “element name” that is described in both a starting tag and an ending tag as a name associated with an element, an “element content” that is described between the starting tag and the ending tag as contents associated with the element, and an “attribute” that is optionally assigned. The element is defined in the DTD (Document Type Definition). In other words, the XML makes it possible to exchange information (a document) by changing a structure of the information into a document type definition file called the DTD. Based on this, users can prepare and use own tags for assigning a method of expressing a document of the information to be exchanged and adding meanings to character strings in the sentence. As explained above, the XML has functions of high-level structural expression and clear contents expression.
Although the XML has such excellent characteristics, when the XML has been leaked out, the contents of the information can be easily analyzed than other expression means. In other words, according to the information exchanges using the XML, a third party can easily estimate the contents of information (a document) based on the DTD and the XML document. Therefore, this method has a problem in that there is a high risk of the contents of exchanged information (a document) being easily stolen by a third party, as compared with the case of information exchanges using the HTML.
As explained above, the conventional systems have various problems. Consequently, they have not been convenient for users, and they have had poor security.